A. Technical Field
The present invention relates to a cement additive, and more particularly, to a cement additive having excellent fluid retainability of a cement composition such as cement paste, mortar or concrete, and further, excellent mortar kneadability.
B. Background Art
Since early deterioration of concrete structures became social problems in 1981, it has been strongly required to improve execution and durability of the concrete structures by decreasing the unit quantity of water in concrete. Thus, a lot of technological innovation is carried out to cement admixtures which have much influence on the quality and the capability of cement mixtures.
Especially, as to polycarboxylic cement dispersants, many proposals were made, because the polycarboxylic cement dispersants exhibit higher water reducibility than conventional cement dispersants such as naphthalenic ones. For example, JP-A-06-321596 and JP-A-06-279082 propose polymers as formed from a (meth)acrylic monomer in which an ester bond between polyalkylene glycol and (meth)acrylic acid is made through propylene oxide. However, even as to these polycarboxylic acids with oxyalkylene groups, it is insufficient to achieve excellent fluid retainability and excellent mortar kneadability.
As to the oxyalkylene group, as things stand, the above known patent publications (JP-A-06-321596 and JP-A-06-279082) disclose only oxyalkylene groups of which the chain length of ethylene oxide as linked to polypropylene oxide is short in acrylic esters.
As is mentioned above, the above conventional cement dispersants have problems in that they lack the fluid retainability and are still insufficient to shorten the kneading time of mortar and concrete.